I just completed this on my Prot Warrior less than a minute ago, so I'd like to give some pointers that helped me out. I'll start with my character's stats:
ilvl 899 Equipped - 44 Artifact traits - Can post a screenshot of gear if requested (Actually I'll just include a screenshot now:
http://i.imgur.com/z5wFqRb.jpg?2 this was during the screen transition after the scenario)
Legendaries used: Bracers + Belt (At this moment this combination yields the best results)
Talents used: 2-1-1-2-1-3-1 (I made a @
Focus macro for Storm Bolt so I could stun Variss/Kruul easily while running and avoiding infernals)
Food used: Bear Tartare (Provided a lot of movement speed which helped a lot, especially during Kruul phase)
Strength flask used of course
Now for the actual tips:
Phase 1 is pretty much the same across most tanks, only take about 4 stacks of debuff, when horrors spawn, tank them just outside the circle so your thunderclap/revenge/AoE in general can still hit Variss. Take care of eyes immediately if you can, but if you're comfortable with having some up, go ahead. They disappear when Kruul lands.
Use orbs sparingly, because you want to transition with 3 orbs up if you can.
For Phase 2, I can only give Warrior-specific tips. The most important one is something that I've already seen in this thread, but its worth mentioning:
Spell Reflect the Twisted Reflection cast. This is important for two reasons:
1. It heals you for a decent amount, while you're taking the obscene amount of damage from green pools on the ground.
2. You don't have to be near Kruul at all to interrupt it, just let it go through with Spell Reflection up since you'll most likely be getting pushed around and avoiding infernals.
Bonus: Annihilate is a physical attack, so it can be blocked/Neltharion's Fury'd
I also used my 2nd potion + Drums of Fury as soon as Kruul became attackable
Kruul only casts 2 things; Twisted Reflection, which we covered, and Annihilate. Annihilate is sort of like the soft enrage of the fight, because it has a stacking debuff and makes you take more damage from it. The goal is to kill Kruul within 3 casts of Annihilate, 4 casts if you use cooldowns to survive the 3rd one (because it does 12mil damage without defensives). You use the orbs to interrupt his Annihilate casts since they cannot be interrupted otherwise.
My strategy for this was to let Kruul cast his first Annihilate for free, make sure to have Spell Reflection ready for each cast of Twisted Reflection (which is easy because he doesn't cast it often). During his 2nd Annihilate cast I keep myself near an orb and pop it right before he finishes his cast. After the disorient, Kruul will immediately cast Annihilate again, at which point I use Storm Bolt to stun him for even longer and get some more damage on him. Kruul will again cast his 2nd Annihilate, which you can let go through but have shield block up at least to reduce some of the damage. Do the same with his 3rd Annihilate cast, delay it with orbs + Storm bolt if its up, but make sure you're ready for it when it finally goes through, Shield Wall should be used for this moment, but you can save it if you're comfortable with just using Nelth's Fury + Demo Shout. By the time Kruul gets to his 4th Annihilate cast, he should be dead.
That's all I can think of and I hope it helps some of you out. It can be done!